Liquefaction and rectification of gases



Dec. 7 192s. 1,609,450

c. c. VAN NUYS LIQUEFACTION AND RECTIFICATION OF GASES Filed Dec. 2, 1919 0 introduction of numerous novel features in CLAUDE Ci V NUYS, OB NEW YOBK, N. Y., IGNOR TO AIR REDUCTION COMPANY,

me, A OOOTION-OF NEW YO :21

LIQUEFACTION AN D BECTIFICATION OF GAQEB.

Application filed December 2, 1819. Serial No. 841,958.

This invention relates to the liquefaction and separation of gases in gaseous mixtures, and particularly to theaccomplishment of v such separation in the most economical manner for the purpose of recovering the constituent ases.

It has een proposed heretofore, and commercial methods are now operated, to separate the constituent gases of a mixture, for example, atmospheric air, by liquefaction and subsequent rectification. Methods, as heretofore practiced have, however, a rela-. tively low efliciency, when compared to the theoretical possibilities, and it is with the object of increasing the eficiency and, therefore, the economy of liquefaction methods that I have undertaken extensive study of the fundamental requirements thereof.

The work required to separate the constituents of a gaseous mixture by liquefaction is made up of certain fundamental'components which are, first, the work of separating the molecules of the constituent gases and bringing the partial pressures'of the respective constituents, when separated, up to -atmospheric; second, the work required to remove heat leaking into the system from external sources and, third, the mechanical losses of the s stem. The first component is a constant br given mixtures of gases, and the second and third depend upon efliciency of insulation and of the mechanical devices employed. Practically, however, a

relatively enormous component has been added to the-total energy expended in liquefaction and rectificationofgaseous mixtures as aresult of irreversible pressure drops, which have heretofore been considered unavoidable. 4 T I I It is the object of my invention to sub stantially eliminate the latter component, thereby approaching more closely the theoretical limit of efiiciency in the separation of constituent gases of a mixture, and to provide an apparatus for the accomplish;

ment of this purpose, thus cheapening the product andrendering it available for extended usage. 'i

A further object of my invention is the a li' uefaction and rectification operation,

- whic render it more nearly automatic and i avoid losses which have heretofore reduced the eflicienc of-such operations.

Other ob ects of my invention are the proindirect contact 'Wit vision of a method of separating the constituent gases of a mixture which rmits the withdrawal of the constituents 1n substantial purity, a result which has heretofore been impossible, because under prior methods one gas is necessarily contaminated with the other to insure relative purity of r the latter gas, and the cycling of the unseparated residual mixture, so that the constituents of all of the mixture are eventually separated, thus avoiding losses which have heretofore arisen as a result of discharging large volumes of gas without separation,

after the pressure thereon has been released,

with consequent loss of available energy. I Another object of the invention is the re.- duction of the total energy consumed in separating the constituents of a gaseous mixture by expanding the gases leaving the apparatus with the recoveryof energy and the cooling of the mixture before com ression toreduce the initial energy require These and other objects and advantages of the invention will be more clearly understood by reference to the following s ecification, when read in connection wit the accompanyingflrawing, in which Ihave tinctive features thereof may-be appreciated,- I shall outline briefly the normal operation of a commercial oxygen apparatus, according to a well known method, described in Letters Patent No. 981,748. Thus, atmospheric air is compressed to a pressure of substantially thirty atmos hens; in a two-stage compressor provide 'with intercoolers and aftercoolers supplied with water, and is thereafter cooledfin temperature exchangers by I gases resultin from the separation. A portion of the coo ed air is conveyed to a liquefier and is cooled there-' in by indirect contact with the.cold se arated gases, beforethe latter pass to t e exchangers The liquid produced in the .liquefier is conveyed pasta pressure reducing valve to a pot at the baseof a rectifi- .cation column- The other portion of the cooled airis conveyed to an expansion ening 'in the lower pot, heretofore refer gine, where it is cooled, by ex ansion with external work to a ressure four to five atmospheres, which 18 the ressure prevailart of t e column. The cooled air from t e en 'ne passes into the to, and thence upwardly through tubes of a vaporizer which contains liquid oxygen resulting from rectification, as hereinafter described, and which is evaporating at a somewhat lower gressure than that of the air in the tubes.v

xygen and some nitroglen are liquefied in the tubes and return to t e pot, mixing with the liquid delivered from the liquefier. The

valve, and 1s discharg compartment of the column, which is propot is divided into two com artments, in one of which the liquid accumu ates as described.

vided with a series of trays, holding a supply of liquid through which ascending vapor ubbles with resu ting progressive enrichment of the vapor in mtrogen. Since the pressure in the vaporizer at the base of the column must be released sufliciently to enable the liquid oxygen contained therein to li uefy the substantially pure nitrogen,-circu ating in the tubes connected to the second compartment, throttli of the liquid by means of the pressure re ucing valve must be column.

resorted to, and this causes an irreversible pressure drop and a serious loss in efii iency as hereinafter explained. The liqui nitrogen from the second compartment is conveyed throu h. a similar pipe and ressure re ucing va ve into the column an is discharged at a point above the inlet for liquid rich in 0 gen. The liquid nitrogen must also be t rottled down to the pressure prevailing in the rectification compartment with a corresponding loss in efficiency. Gaseous oxygen is withdrawn from the vaporizer, and nitrogen, mixed with more or less oxygen, escapes at the top. of the The gases are separately conveyed through the liquefier and exchanger to cool the incoming air by transfer of heat to the outgoing 'a:

Itwill appreciated as this description proceeds that, while the method described is the most veiiicient heretofare known, for the purpose, it is subject to a number of disadvantages, which prevent the highest efliciency, and which I propose to overcome as great ex nse, the products of the se aration are disc arged at-a pressure below t re at mospheres without recovery of energJ for three to four per cent delivere by t e expansion engine, andonly one gas is recovered in a substantially pure condition, the other, in this ase, nitrogen, carrying upward tosix per cent of oxygen. The

of nitrogen require by the composition of air, amounts to substantially twenty-four per cent of the air originally entering. the apparatus, and isd scharged with the remaining nitrogen to the .atmosphere. A relativel large portion of the air escapes, there ore, after compression, cooling, etc.,

without so aration, and' represents a mate' rial loss 0 energy.

I havev disdovered that the causes for the large loss of oxygen in the vapors leaving the top of :the rectification column are not due. to mechanical imperfections of the a paratus, but are inherent in the recti cation method, which requires the liquefaction of all of the semis mixture. .In any rectification met od, maximum efiicienc requires that the relative amounts of ascen in vapor and descending liquid in the not cation column be such, that at the top and bottom the vapor has a composition closely aproach ng that necessary for base eqvq ilibrium with the liquid at those evels. e may assume that .the composition of the exce t hereinafter set forth. For example, althrough the gaseous mixture is primarily compressed to about thirty atmospheres at mixture of this oxygen with the proportion first or liquid rich in oxygen includes substantially forty-seven per cent, of oxygen. This is the liquid composition necessary for phase equilibrium with the incoming air at the base of the column, and thus repre-. sents the maximum possible enrichment in oxygen attainable without further rectification.

If any of the second or high nitrogen liquid be admitted to the rectification chamber above the inlet for liquid rich in oxygen, it is certain, ifpure oxygen is to be obtained, that the upward passi vapor must vaporize an amount 0 this iquid equivalent to its nitrogen content, bein in part liquefied thereby. The result of tfiis liquefaction of the upwardly passing vapor is the production, at the entrance level of the first liquid,

of a downwardly flowi liquid which is enriched in oxygen. The hmiting composition of this liquid will be the same as that of the first liquid and will be attained only if the amount of the upwardly passing. vapor liquefied by the second liquid entering at the definite amount.

In the method under discussion, the

amount of available nitrogen liquid is in excess of that required to produce the equitop of the rectifier doesnot exceed a certain iference between the condensation pressures librium composition at the lower inlet and if we allow nothing but pure'nitrogen to escape at the top, the liquid passing downwardly will contain all of the oxygen of the ori 'nal air mixed with 4 to 5% of argon wh ch must appear at the bottom of the rectification chamber. On the other hand, if we vaporize an amount of liquid suflicient to insure the production of nothing but pure oxygen at the bottom, the amount of downwardly flowing liquid is insuflicient to liquefy the oxygen in the vapor and oxygen Wlll appear at the top. It is apparent, therefore, that it is impossible to obtain pure oxygen without considerable loss-of oxygen in the eifluent gas from the operation of this method if all of the nitrogen liquid is'admitted at the top of the column.

The losses in the method described, which are due to throttling have already been mentioned. We have seen, for example, that the pressure in the rectification column must be low enough to enable liquid oxygen I at the reduced ressure to condense pure nitrogen at a bi er pressure inside the ver tical' tubes of the vaporizer, this difference of pressure bein accomplished by ithrottling through 51c two pressure reducing valves employed, and thatall of the nitrogen is liquefied. .1

To separate a mixture of two gases into its consituents, the theoretic m nimum of work required depends upon the partial pressures exerted by the two constituents during an isothermal compression of each constitutent up to a pressure equal to that exerted by the mixed gases, by means of a piston impermeable to} one and permeable to ,the other. This Work is thus independent of the difof either constituent at any temperature. If the diflerence of pressure maintained between opposite sides of an expansion device is such'thatthe loss of available energy in the fluid mixture, because of the lowering of the ressure thereof,-is just equal to the theoretic work of separation, then, since the latter work is theoretically recoverable, the whole operation is reversible and it will be just possible theoretically to completely separate the two constituents, by reversibly lowering 'the pressure on all the liquids pro.- duced to .the pressures required. If, how-. ever, the loss of available energy by the lowering of pressure is greater than the theoretic work required for separation, there is a net amount 0 available energy expended by that operation.

In this discussion, the assumption is made that the lowering ofpressure upon the liquidis accompl shed reversibly, i. e., this-decrease of pressure occurs by, reason. of the liquid acting as the working substance of an ideal adiabatic engine or liquid motor and thus. the dissipation of available energy resulting in the actual case from the irreversible expansion through the reducing .valves, is neglected. This dissipation of available ener is regarded as inevitable on account of t 1e impracticability of employing a reversible engine to expand the liquid under the conditions prevailing.

The excess liquid throttled in rectification by the method described in which all of the liquid is throttled over and above that amount necessary to accomplish complete separation, carries a definite amount of available energy, which becomes irrecoverable. This dissipation 'of available ener reduces the efliciency of the method and thus adds to its cost of operation. The efiiciency of the method is further reduced by throttling the liquid produced in the liquefier from the pressure delivered by the compressor down to that prevailing inside the. lower end of the column.

I have discovered that these difficulties may be readily overcome and that the liquefaction and separation of gaseous mixtures may be improved to eliminate many of the losses heretofore experienced. My improved method-will first be outlined to give a general view thereof, after which the details of operation. will be clearer and will be more fully set forth with reference to the draw- @rimarily, my invention rests upon the idea of liqueiying only a portion of a gaseous mixture, this being accomplished at the initial pressure, i. e., as delivered by the compressor. The mixture treated may, for purposes of' illustration, be considered as air,

although the same principles are applicable to other aseous mixtures. 'The portion li uefied w1ll carry all of the oxygen contamed in the original mixture, together with some of the nitrogen and argon the theoretical possible upper limit of oxygen content in the liquid being substantially 47 'per cent, which is the composition of liquid necessary for phase equilibrium with vapor of air composition. The remaining gas consisting substantially of nitrogen, and argon will be withdrawn from the apparatus at the initial pressure. The nitrogen, which will carry a small'amount of argon, maybe used for any oft-lie purposes tofwhich it is adapted without further rectification or other treatment.

The liquid portion will then be rectified- .by subjecting it in a suitable column to dlrectcontact .with vapors arising from a vaporizer, containing substantially pure liqu d oxygen resulting from the rectification. The evaporating oxygen serves, by heat interchange, to

liquefy a portion of the incoming air as hereinbefore explained, and the rectifying column may be maintained .at-- a..-pressu re somewhat below that of thepfmcoming a r,

the difference in pressure produced the necssary throttling of the liquid discharged mto the column from the receptacle in w ich it is accumulated. This difference of pressure between the liquid oxygen surrounding the vertical tubes of the vaporizer and the gases passing u ward in those tubes must be sufiicient to ena le liquid. oxygen to 'rated' into its constituents.

cause, by indirect contact, condensation of the ascending gases in said tubes. I do not ropose, however, to liquefy the substantialy pure nitrogen leaving the top ofthe tubular s stem, and it is clear, therefore, that a smal or degree of .throttling of the li aid will be required, thanis necessary in car 121' methods where the liquid ox gen is called upon to condense substantia y pure nitro- Since the composition of the liquid discharged into the column is substantially that determined by phase equilibrium with gaseous air, the eflluent from the to of the recreason of the throttling operation upon this liquid becomes as nearly equal as possible to the theoretically recoverable work of completely separating the two constituent gases of the mixture treated, i. e., the whole operation is rendered as'nearlv reversible as is practicable and hence its thermodynamic.

efiiciency will approach as closely as possible the theoretic maximum.

Substantially pure oxy n is withdrawn from the vaporizer, herein fore referred to, and because of the simplification of'the rec-v tifying 0 eration, it is possible to produce oxygen 0 a purity of 99 per-cent .or better, without excessive loss of oxygen, a result which has not been heretofore achieved. The oxygen escapes at a pressure somewhat below the initial pressure and may be stored and i used in the ordinary manner.

' ofv liquefaction at the initial pressure and In carrying out 'my method, I utilize and extend the principle of expansion after liquefaction as described and claimed-in thefiplication for Letters Patent of Montague Roberts and Claude C. Van Nuys,Serial No. 280,515, filed March 4, 1919, patented May 12, 1925, No. 1,537,193. This -applica-.

tion involves the discovery of the advantages subsequent expansion of the separated products. 'As has been previously noted,

t e ni-v trogen is delivered fromthe column diF the oxygen and eflluent air escape at a slightly initial pressure of the incoming air and the lower presure. These gases are very cold and of substantially the same temperature. The low temperature is transferred to incoming ai and the gases thus warmed and at high pressure are capable of expansion, in

suitable engines, to recover a large part of the energy, originally expended in bringing the air to its initial pressure. This. energy may be employed in compressing further quantities of air, the energynlost in the apparatus being made up rom an external source. Preferably only the nitrogen 'and oxygen are thus expanded in carrying out my method. The low temperature of-thescgases, developed by expansion, is utilized in cooling the column and interchangers to make up li uid evaporated by the heat leak age throng the walls thereof.

'1 also utilize and extend the principle of cooling of the incoming gaseous mixture priorv to compression as described and claimed in the apfilication for Letters Patent of Montague Roberts and Claude C. Van Nuys, Serial No. 289,099, filed April 10, 1919. The latter application involves the discovery that the work required in compressing a quantity of gas corresponding to a predetermined eflluent volume is reduced if the gas is cooled prior to compression. 1, therefore, employ an exchanger of temperature, in which the air prior to primary com-.

pression is subjected to heat interchange with a cold gas leaving the system, this arrangement making it ossible to utilize eiiiciently any excess re rigerant efiect of the system over and above that necessary to maintain the low temperatures required in the liquefaction operation. The air thus cooled is compressed, preferably in a single stage compressor, and is cooled an intercooler sup lied with circulating water.

As note the eflluent air from the column is at high pressure, and, even afterits heat interchange with incoming air, is still at low temperature. I propose to mix thi's eflluent. air with the incoming air from the first com ression, thus cooling the m'xture, which is t en further compressed to the desired pressure, preferably in a single stage compressor. After bemg cooled in .an'.-after- 'cooler supplied with circulating water, the

incoming air passes to the exchanger for further cooling by the gases from the column beforeentering the latter. By operating as described and avoiding as far as all irreversible temperature drops -media at widely varying temperature, I am tween enabled to closel approach the theoretically possible therm namic efliciency in a liquefaction system, tlius reducing materially the cost of recovering the constituent gases.

, In starting the operation, the apparatus is, v of course, at atmospheric-temperature and ssible neoaaeo there is no liquid ale-ad, to that a is necessary to reduce the tem erature of the ap paratus to that required orliquefaction and ciently cooled and a supply cf liquid has accumulated.

The details of o ration, includin starting,fwill be more c early understood y reference to the drawin The rectification column comprises a she I 5 divided by partitions 6, 7 and 8 to provide apot 9, a gas chamber lO, a liquid chamberll, and a'rectification chamber12. A plurality of tubes 13, passing through the a'rtitions 6 and 7 and terminating in a bee 14, are adapted to permitpassage of gas from the pot 9 to the,

head, 1n indirect contact with is in the chamber 10 and liquid in the chem r 11. A

. plurality of baflies,1 5are disposed within liquid accumulates as hereina T the chamber 10 to direct the passage of gas therein downwardly and about the tubes 13, and a supplemental receiver 16 for liquid is supported within the chamber 11 so that liquid ovcrflowin therefrom collects in the bottom of the c amber. The rectification chamber 12 is provided with a plurality of battles 17 having gas outlets 18 and caps 19 which permit the upward passage of gases through the baffles and the layers of liquid are maintained thereon.

This liquid is delivered to the rectification chamber 12 through a pipe 20, having a pressure reducing valve 21 therein and communicating with the bottom of the 0t 9 in which r described.

e liquid flowing downwardly over' the baflies 17 gradually gives up its more readily vaporizable constituent and is finally de-,

livered through a pipe 22 to the receiver 16.

The liquid in the receiver 16 is evaporated by heat transferred from gas assing through the tubes 13 and the vapor t us released passes upwardly. through the rectification chamber 12,- where it is joined by the more readily vaporizable constituent released from the liquld, while the more readily liquefiable constituent therein joins the liquid flowing down through the rectification chamber and is returned to the receiver 16.

The gaseous effluent/escapes from the rectification chamber 12 through a pipe 23. The liquid accumulating in the bottom of the chamber 11 comprises one of the constituents of the gaseous mixture treated, in a substantially pure condition and, being vaporized by heat derived from the gaseous mixture passin through the tubes 13, it escapes through a pi e" 24. The gaseous mixture. to 'beliquefied and separated, is

delivered to the pot 9 through a pipe .25 and in passing through the tubes 13, a portion only of ,the gas is liquefied and drops into the t, the residual gas being delivered to the ead 14 and escaping through a pipe 26.

There are thus three separate gases delivered from the column and if air is the gaseous mixture treated, the efiuent gas delivered through the pipe 23 will havesubstantially the oompodtion of air, while substantiall pure oxy n and nitrogen are respective y delivere through the pipes 24 and 26. These gases are extremel 75 cold and serve as a cooling medium fort e incoming gaseous mixture.

-I, therefore, provide an exchanger 27 in which the incoming g ous mixture is subjected to heat interchange with the. various products of the column. The exchanger comgrises a shell 28 divided into sections A, C: and D, each section comprising a plurality of tubes-29 and 30 and a plum l'ty of bafiles 31 which cause the incoming gase-. ous mixture surrounding the tubes to travel back and forth across the section as it advances. The pipe 25 is connected to the section A of the exchanger so that the ous mixture, after circulating about the bafiles 31, is delivered thereto-and thence'to the potv 9. The pipes 23 and24, and a pipe 32 communicating with the chamber 10, of the column, are connected to chambers 33,

34 and 35 at one end of the section A of the exchanger with each of which a number of tubes 30; communicate. The plpe 26.1s similarly'connected to a chamber 36 'atthe end of the section A' with which the gipes 29 communicate. Thus, all of the pro ucts of the column are separately delivered to and pass through the tubes 29 and 30 in indirect contact with the incoming gaseous mixture. 7

The tubes 30 of section A deliver the several Ll mm to chambers 37 38 and 39, intermediate sections A and T3 of the exchan r and thence to the tubes 30 of section The gas passin through the tubes 29 in the section A. is de vered to a chamber 40 and thence through a-pipe 41 to a cham- A portion of the gas, which .in the treat-' I ment of air, is substantially pure nitrogen" is withdrawn through a p1pe 50, controlled by a valve 51, and is delivered to an engine 52 where it is expanded with external work andthereby cooled. Thence the gas passes through a i e 53 to the chamber 10 of the column an t e cold produced by expansion 1o 4 communicate. Tubes 29 of section C comis utilized therein in the preliminar liqueof section C communicate.

as has passe he tubes 30 deliver the gases passing thereutilized in coolin faction of the gaseous mlxture. e cold gas circulates about the baflles 15 and escapes through the ipe 32 to the exchanger.

From the c amber 45 of the section B of the exchanger, the as is conveyed through a pipe 54 to a chamber 55, with which tubes A pi 5e conveys s from the chamber 46 to a c amber 57 with which tubes30 of section 0 also municate with the chamber 49 receiving a portion of the gas from the chamber 47. A pipe 58'conveys gas from the section 0 of the exchan er to the section B, after the d about .the baflles 31 therein.

through to chambers 59 and 60 intermediate the sections 0 and D of the exchanger, and the tubes 29 deliver the gas conve ed thereby to a chamber. 61. The gas -from t e chamber 61 is delivered through a ipe .62 to a chamber 63 in the section B of the exchanger. The tubes 29 of section D com municate with the chamber 63 and the tubes 30 with the chambers 59 and 60. The gaseous mixture in the section D escapes through a ipe 64 to thesection C. The gases are 'de ivered by the pipes 29 to a chamber 65 and by the ipes 30 to chambers 66 and 67 at the end 0 the exchanger.

From the chambers 65, the gas, which, in

the treatment of air, is substantially pure.

nitrogen is withdrawn through a. pipe 68 controlled by a valve 69 and is delivered to an engine 70, where it is ex anded with external work and is delivere through a ipe 71 to the chamber 57 of the exchanger w ere it mixes with the gas previousl in the engipe 52 and enterin t rough the pipe 56. he cold produced y the expansion of the gas in the engine is thus the incoming gaseous mixture. A portion of this cold gas is drawn from the engine 70 to a pipe 72 controlled by a valve 73 and is delivered to an exc anger 74 as hereinafter described.

Gas from the chamber 66 at the end of the exchanger, which, in the treatment of air is substantially pure oxygen, is withdrawn through a pipe 75 controlled by a valve 76 and is delivered to an engine 77 where it is expanded with external work and expanded 86 and 87. The incoming gaseous mixture I 83 from which they escape through pipes' is thus-cooled b indirect contact with cold roducts from t e column and the precool- 111g thus accomplished causes a preliminary condensation o the gaseous mixture. Thus it is possible for the compressors, as hereinafter described, to handle a considerably greater volume of gas than would bepossible if the gas entered atinorma'l atmospheric temperature.

The cold gaseous mixture is delivered from the pipe 85 to a single stage compressor 89, where it is initiallyv compressed. The' compressed gaseous mixture escapes through a pipe to an intercooler 91- in which the gaseous mixture is cooled by indirect contact with water. Thence the gas passes through a pipe 92 to .a compressor 93. A pipe 94 controlled by a valve 95 conveys gas which. in the treatment of air, is the efiluent, escaping from the top of the rectification column and having substantially the composition of air, to the pipe 92 where it mixes with the incoming gaseous mixture. The gas delivered through the pipe 94 is very cold and serves, by mixing with the incoming compressed gaseous mixture to precool the lat- Y ter in a manner similar to the precooling in the exchanger'74 with a corresponding effect u on the capacity of the compressor 93. rom the compressor 93 the gaseous mixture is delivered to a pipe 96 to an-aftervcooler 97 where it is subjected to the cooling action of water and is thence conveyed to a pipe 98 to the section D of the exchanger 27. In the exchanger, as previously de'- scribed, the gaseous mixture is cooled by heat interchange with the various products of the column and is finally delivered at an extremely low temperature through the pipe '25- to the pot 9. The gas in the-chamber 67 at the end of the exchanger 27" which.

has been previously expanded in ,the engines 52 and 70, escapes through a pipe .99.

obviously-in startingthe operation, the entire system is at atmospheric temperature and the desired low tem erature must be established by the expansion of the previ ously compressed gaseous mixture. For this purpose I provide aby-pass 100 controlled by a valve 101 and connecting the ipes 50 and 94 and a by-pass 102 controlled y a valve 103 connecting the pipes 72 and v 78. In starting, the valves 101 and 103 are opened and the valves 73, 79nd 95 are osed, while a valve 104 in the pipe 71 is opened fully, it being partially closed in normal operation.

The gaseous mixture, after compression and passage through the exchanger 27, enters the column through the pipe'25. A

portion thereof escapes through the'pipe 23 and another ortion leaves through t e pipe 24, the remainder being delivered through the gipe 26. The as'eous mixture reentering t e exchanger 2 from the pipe 26 passes through the tubes 29 of sections A and B and a portion is withdrawn and ex ended in the engine'52, and is thereby coole Thecooled gaseous. mixture passes through the pipe 53 to the chamber causing the progressive cooling. of the incoming gaseous mixture in the tubes 73. The gaseous mixture escaping from the chamber 10 throu h the pipe 32 travels through tubes 30 of t e exchanger and is finally delivered through the pipe 99.

Another ortionof the gaseous mixture from the pipe 26 is withdrawn, after passage through the tubes 29 of sections C and D of'the exchanger, and is delivered through the ipe 68 to the-engine 70 where it is expan ed and thereb gaseous mixture from the pipe 24 after passing through the tubes 30 in all sections of theexchanger 27 is delivered by the pipe 75 to the engine 77 where it is expanded and cooled. The cooled gaseous mixture is delivered throughthe pipe 78, b -pass '102 and pipe 72 and 71 to the exc anger 27,

mixing with the ex anded gaseous mixture from the en'ne 70 and after passin through the tus 30 in sections C and D o exchanger 27, the gaseous mixture escapes through the pipe 99.

It-will be apparent that in starting, all of the gaseous mixture is expanded after compression and that cooling of the gaseous mixture is thus progressively carried on until the desired low temperature is attained and liquid is deposited in the pot 9. The method is particularly effective in startin the temperatures falling rapidly so that t e method is in full operation in a much shorter time than is possible with previously known methods. Of-course, when the desired temperatures have been attained the'valves are readjusted to the normal working conditions panded in a suitable engine to recover the as previouslydescribed.

'VVith thearrangement of the ap aratus clearly in mind, it will be apparent t at the proposed method of liquefaction involves numerous novel principles which distinguish it from methods heretofore employed in the that air is being treated, it will be noted that the air is subjected in the column to} cool- I ing by indirect contact, 'fi"st, with the cold gaseous product and subse uently by contact with an evaporating liqui so that the more liquefiable constituent is separatedand flows into the pot 9, while the residual gas which is substantially pure nitrogen passes off through the pipe 26. During the liquefaction operation, there is no release fromthe pressure of the gaseous mixture and consequently the nitrogen esca es from the column at its initial pressure an after giving up its cold, it is expanded in suitable engines to recover a large pro ortion of the energy originally employed 1n bringing the gaseous mixture to the initial ressure. The nitrogen is, moreover, with rawn from the cycle, so far as the further treatment of the'gaseous mixture is concerned and is never'lique fied. The liquid accumulating in the pot 9 is substantially 47% oxygen and is delivered in p til

through the pipe 20 with slight throttling by the valve 21 to the rectification chamber 12 of. the column.

The eflluent gas escaping throu h the pipe 23 from the column has the equili rium composition for a liquid such as is deposited in the pot 9 and consequently this eflluent gas corresponds in composition to atmospheric air. The efliuent gas is extremely cold and after passing through the exchanger it may be discharged to the atmosphere through a valved outlet 93. owever, as abovenoted,

it is preferably em loyed while still in a cold condition and a a pressure of the upper part of the column to precool the gaseous mixture before the latter passes to the second compressor. The liquid passing down through the rectification compartment 12 meets vapors arising from the liquid in the recepta'cle'16 so that nitrogen is gradually separated from the li uid which finally arrives in the bottom of t e chamber 11 as substantially pure liquid oxygen. The liquid is portion of the energy originally expended in compressing the incoming air, the recovery of energy from this source when combined with that recovered by the expansion of nitrogen. delivered from the column, comprising '.the major portion of the energy originally employed in compressing the air.

The energy recovered n the various engines in starting as well as in normal operation, may be utilized in driving the compressors and inasmuch as the energy recovered is a material proportion 0 that employed in the" initial compression-there is a marked saving in operation. Precooling of the gas before compression introduces a further saving and the elimination of one constituent, for example, nitrogen, without li uefaction completes the possible economic a vantages to be efl'ectedin a liquefaction operation.

The pressures and temperatures attainedin the practice of the method will depend upon well known principles of liquefaction and wiIl vary with gaseous mixtures of different character. It will not be necessary,

\ however, to employ initial pressures as high as has been heretofore essential, nor will the temperatures be so low as is required when all of the aseous mixture treated must be liquefied. ecause they are subject to wide variation no attempt is made hereinto set forth in detail the pressures and temperature employed. It is suflicient to note that in the treatment of air, initial pressures upward to '30 atmospheres will'be quite sufiicient and that a temperature well above the critical temperature of nitrogen may be developed for example-156 C. in the liquefaction zone.

I am aware that various changes ma be made in the method herein described wti out departing from the invention or. sacrificing any of its material advantages and I desire, therefore, to claim broadly all of the steps and combinationsthereof whereby the.

effective separation of gaseous mixtures in accordance with my method is accomplished.

I. cla1m:-

1. In the separation of the constituents" of a gaseous mixture the method whichcomprises subjecting the mixture to a hquefyin operation whereby a liquid containing sai constituents is formed, leaving a portlon of one of said constituents as a residual as, withdrawing and expandin gas, causing it to travel in mdirect contact with the gaseous mixture to be liquefied, rectifying-the liquid produced by the liquefying operation to produce a liquid containing one of the constituents in substantial purity and an eflluenthaving substantially the composition of the original gaseous Y mixture, vaporizing the liquid thus produced and separately I withdrawing the vapor and the eflluent. a

2. In the separation of the constituents of a gaseous mixture, the method which comrises, subjecting the mixture to a liquegyingo eration whereby aliquid containing sai constituents is formed, leaving a portion of, one of said constituents as a residual gas, withdrawing said residual gas, rectifying said liquid, warming said residual gas by heat interchange with said mixthe resi ual ture, successively ex anding' separate portions of said residua gas and utilizing the cold expanded product to maintain the i quired low temperature. I

- 3. In the separation of the constituents of a gaseous mixture, the method which comprises, subjecting the mixture to a liquefying o eration whereby a liquid containing sai constituents is formed, leaving a portion of one of said constituents as a residual gas, withdrawing said residual gas, rectifying said liquid, evaporating the liquid product of the rectification, warming the evaporate and said residual gas by heat interchange with said mixture, se arately expanding said evaporate and resi ual gas and utilizing the cold expanded products to maintain the required low temperature.

4. In the separation of the constituents of a gaseous mixture, the method which comprises, subjecting the mixture to a liquefying o eration whereby a liquid containing sai constituents is formed, leaving a portion of one f said constituents as a residual gas, with rawing said residual gas,

.the evaporate and residual gas by heat interchange with said mixture, expanding said evaporate, successively expanding separate portions of said residual gas and utilizing the cold expanded products. to maintain the required low temperature.

5. In the separation of the constituents of a gaseous mixture, the method which comrises, subjecting the mixture to a liquei' ying operation, whereby a liquid containing said constituents is formed-, leaving a portion of one of .said constituents as a residual gas, withdrawing said residual gas, rectifying said liquid, and withdrawing an efiluent gas following rectification, said effluent gas having substantiall the composition of said mixture. 1

6. In the separation of the constituents of a gaseous mixture, the method which comios rises, subjecting the mixture to a liqueying o eration whereby a liquid containing sai constituents is formed, leaving a portion of one of said constituents as a residual gas, withdrawing said residual gas, rectifying said liquid, withdrawing an effluent gas following rectification, said efiiuent gas having substantially the composition of said mixture and cyclin said eflluent gas with further quantities 0 said mixture.

7. Inthe separation'of the constituents of a gaseous mixture, themethod which comprises, subjecting the mixture to a liquefying o eration whereby a liquid contain? ing sai constituents is formed, leaving a portion of one of said constituents as a residual gas, withdraw-ing saidresidual gas, rectifylng said liquid, withdrawing an efiiuent' gas following rectification, said eliiuent gas having substantially the composition of said mixture, and adding said efllue'nt gas to said mixture after the latter has been initially compressed.

8. In the separation of the constituents of a gaseous mixture, the method which comprises, subjecting the mixture to a lique- :fying operation whereby a liquid contain-,

mg said constituents is formed, leaving a portion of one of said constituents as a residual gas, withdrawing said residual gas, rectifying said liquid, withdrawing an efiluent gas followin rectification, ,said

eflluent gas having su stantially the composition of said mixture, warming saidv etiluent gas by heat interchange with said mixture and adding said'efiluent gas to said mixture after. the latter has been initially compressed.

9. In the separation of the constituents of a gaseous mixture, the method which comprises, subjecting the mixture to a liquefying o oration whereby a liquid containing sai constituents is formed, leaving a portion of one of said constituents as a residual gas, withdrawing said residual gas,

rectifying said liquid, withdrawing an efiuent gas following rectification, said efiuent gas having substantially the composition of said mixture, evaporating the liquid product of the rectification, expanding the evaporate and utilizing the cold of said eiiluent gas and evaporate to reduce the external work of compressing the mixture.

10. In the separation of the constituents of a gaseous mixture, the method which comprises, subjecting the mixture to a liquefying operation whereby a liquid, containing said constituents is formed, leaving a portion of one of said constituents as a residualgas, withdrawing said residual gas, rectifying said liquid. withdrawing an effluent gas following rectification, said eflluent gas having substantially the coin osition of said mixture, evaporating the l quid product of the rectification, conveying the evaporate and said efiuent gas in heat interchanging relation with the mixture, expanding said evaporate and utilizing the cold of said evaporate and efiluent gas to reduce the external work of compressing the mixture.

11. In the separation of the constituents of a gaseous mixture, the method which compr ses, subjecting the mixture to a liquefying o eration whereby a liquid containing sai constituents is formed, leaving a portion of one of said constituents as a residual gas, withdrawing said residual gas, rectifying said liquid, withdrawing an ef aeeo ' 12. In the separation of the constituents of a aseous mixture, the method which comprises, subjecting the mixture to a' lique- Vfying' operation wherebya liquid containing said constituents is formed, leaving a portion of one of said constituents as a residual gas, withdrawing said residual gas, rectify; mg said liquid, evaporating the liquid product of the rectification, warming the evaporate b heat interchange with saidmixture, expan ing the evaporate, utilizin the cold expanded product to cool said mixture before initial compression thereof, withdrawing an effluent gas following said rectification, said eiiluent gas having substantially the composition of said mixture and adding said efliuent gas to said mixture after said initial compression.

13. In .the separation of the constituents of a gaseous mixture, the method which comprises, subjecting the mixture to a liquerectifying said liquid, to produce 'a liquid- 'consisting" substantially of one constituent of said mixture and an eifiuent gas having substantially the composition of said mix-' ture. 14. In the separation of the constituents of a gaseous mixture, the method .which comprises, subjecting the mixture to compression, then to heat interchange, first with gaseous separation products, and then with liquid separation products to liquefy a portion of said mixture leaving a residual gas, withdrawing said residual gas and subjecting the liquid to direct contact with vapors arising from a body thereof to se arate an efiiuent gaseouslpnoduct having su stantially the composition of said mixture.

15. In the'separation of the-constituents of a gaseous mixture, the method which comprises, subjecting the mixture to compression, then at'the pressure developed to heat interchange, first with gaseous separation products, and then with liquid sepa, ration products to liquefy a portion of said mixture leaving a residual gas, withdrawing said-residual gas, rectifying the liquid produced to separate an efliuent gas havin subfluent gas following rectification, saidefllu-- heat interchange, first with gaseous sepaent gas having substantially the composition of sa d mixture,- and adding said efiiuent gas to said mixture after initial and before final compression thereof.

ration products, and then with liquid sepa-- ration products to liquefy a portion of said:-

mixture leaving a residual gas, withdrawing said residual gas, rectifying the liquid produced to se arate an effiuent gas having comprises, subjecting the mixture to compression, then to liquefaction at the pressure developed to separate a liquid from a residual gas consisting substantially of one of said constituents, wlthdrawmg said residual as at said pressure, warmlng. said gas bv eat interchange with said mixture, expan ing said gas to recover the energy stored therein, rectifying the liquid to separate another constituent as a liquid, evaporating the latter liquid, warming the evaporate by heat interchange with said mixture and expanding said evaporate to recover the ,energy stored therein. p

'18. In the separation of the constituents of a gaseous mixture, the method which. comprises, liquefyin a portion of said mixture leaving a resi ual gas consisting substantially of one constituent, expandin the residual gas, causing it to travel in. in irect contact with the gaseous mixture to be liquefied, rectifying the liquid produced to-enrich the latter in another constituent, eva crating the enriched liquid and separate y withdrawin the two constituents and an unseparate mixture thereof having substantially. the composition of the original mixture. I

19. In the separation of the constituents of a gaseous mixture, the method which comprises, separating a residual gas consist ing substantially of one constituent, by liquefying a portion of said gas with the remaining constituents, expanding the residual gas, causing it to-travel in indirect con tact with the gaseous mixture to be liquefied, rectifying the liquid to separate therefrom an efiluent mixture containing both constituents, thereby leaving a' new liquid consisting substantially of a second constituent, vaporizing the latter liquid and separately withdrawing the two gaseous coustituents and said efiiuent mixture having substantially the composition of the original mixture.

20. In the separation of the constituents of a gaseous mixture, the method which comprises, separating a residual gas 'consisting substantially of one constituent, by liquefying a portion ofsaid gas with the remaining constituent, rectifying the liquid to separate therefrom an efiluent mixture containing both constituents in substantially the roportions of the. original mixture,

there y leaving anew liquid consisting substantially of a second constituent, va rizing the latter liquid, separately with rawihigthe two gaseous constituents and said e uent mixture, and adding said effluent mixture to the incoming orlginal mixture.

21. In the separation of the constituents of a gaseous mixture, the method which comprises, refrigerating said mixture 'to se arate a residual as and a. liquid, rectifymg the liquid and thercby separating an effluent corresponding in composition to the original mixture and cycling said etiluent to ensure ultimate separation of the constit uents thereof. 1

22. In the separation of the constituents of a gaseous mixture, the method which comprises, cooling said mixture, subjecting the cooled mixture to COHIPIGSSIOH. 1n independent stages, adding a cold product of the separation to said mi'xture'between said stages and sub uently subjecting said mixture to a lique ying operation. 7

23. InQthe separation of the constituents of a gaseous mixture I the method which comprises, cooling said mixture, subjecting the cooled mixture to compression in independent stages, adding a cold product of the separation to said mixture between said stages, subsequently subjecting said mixture to all ue 'n o eration, whereby a liquid and a'resi ua gas are produced, withdrawing said residual gas and rectifying said liquid.

24. In the separation of the constituents of 'a gaseous mixture, the .method which comprises, subjecting said mixture to compression in two sta es, then to a liquefaction operation, wit drawing and utlliaing cold products of-said operation to cooT- the mixture after final compression thereof,.ex-

pending said products balancing said li uefaction operation by 'vertmg more or ess of the expanded product to cool said m1x- 'ture before initial and after final compression thereof and adding another cold product to said mixture after initial compression thereof. I

25. In the separation of the constituents of a gaseous mixture, the method which comprises, subjecting said mixture to a liquefaction operation to produce two products consistin respectively of two constituents and a third gaseous product corresponding substantially in composition to the original mixture, transferring heat from the mixture to .said roducts, expanding the first two roducts CLAUDE C. VAN NUYS.

recover the energy storedtherem and adding the third gaseous prod- 

